This ETF has lagged the S&P 500's performance over the past decade, but maybe the future will be different.The S&P 500 deservedly gets all the attention, as the index has a total market capitalization of $57 trillion. However, investors need to realize that there is a sea of other companies on the other end of the spectrum that are much smaller than the businesses you're familiar with. Here's where the Russell 2000 comes into the picture. Owning an exchange-traded fund (ETF), such as the Vanguard Russell 20 ...